Xamarin Android ExpandableListView Example

MainActivity.cs

using System.Collections.Generic;
using System.Linq;
using Android.App;
using Android.Content;
using Android.Widget;
using Android.OS;
using Android.Views;
using Object = Java.Lang.Object;

namespace Droid.Sample
{
    [Activity(Label = "Droid.Sample", MainLauncher = true, Icon = "@drawable/icon")]
    public class MainActivity : Activity
    {
        private RelativeLayout _relativeLayout;
        private ListView _listView;

        protected override void OnCreate(Bundle bundle)
        {
            base.OnCreate(bundle);

            AddViews();
            ConstrainLayout();
            SetContentView(_relativeLayout);
        }

        private void ConstrainLayout()
        {
            _relativeLayout.ConstrainLayout(() => 
                _listView.Top == _relativeLayout.Top &&
                _listView.Left == _relativeLayout.Left &&
                _listView.Right == _relativeLayout.Right &&
                _listView.Bottom == _relativeLayout.Bottom
                );
        }

        private void AddViews()
        {
            _relativeLayout = ViewUtils.AddRelativeLayout(this);
            _listView = GetListView(_relativeLayout);
        }

        private ListView GetListView(RelativeLayout parent)
        {
            var listView = new ExpandableListView(this);
            parent.AddView(listView);
            var items = new List<MyThing> {new MyThing("Item 1"), new MyThing("Item 1"), new MyThing("Item 1"), new MyThing("Item 2"), new MyThing("Item 3"), new MyThing("Item 3")};
            listView.SetAdapter(new MyAdapter(this, items));
            return listView;
        }
    }

    public class MyThing
    {
        private static int _intCount = 0;

        public MyThing(string name)
        {
            Name = name;
            Id = _intCount++;
        }

        public int Id { get; set; }
        public string Name { get; set; }
        public int Amount { get; set; }
    }

    public class MyAdapter : BaseExpandableListAdapter
    {
        private readonly Context _context;
        private readonly List<MyThing> _myThings;
        private List<IGrouping<string, MyThing>> _myThingsGrouped;

        public MyAdapter(Context context, List<MyThing> myThings) : base()
        {
            _context = context;
            _myThings = myThings;
            _myThingsGrouped = myThings.GroupBy(i => i.Name).ToList();
        }

        public override Object GetChild(int groupPosition, int childPosition)
        {
            return null;
        }

        public override long GetChildId(int groupPosition, int childPosition)
        {
            return childPosition;
        }

        public override int GetChildrenCount(int groupPosition)
        {
            return _myThingsGrouped[groupPosition].Count();
        }

        public override View GetChildView(int groupPosition, int childPosition, bool isLastChild, View convertView, ViewGroup parent)
        {
            var myThing = _myThingsGrouped[groupPosition].ElementAt(childPosition);
            return new TextView(_context) { Text = myThing.Name + " (" + myThing.Id + ")"};
        }

        public override Object GetGroup(int groupPosition)
        {
            return null;
        }

        public override long GetGroupId(int groupPosition)
        {
            return groupPosition;
        }

        public override View GetGroupView(int groupPosition, bool isExpanded, View convertView, ViewGroup parent)
        {
            var group = _myThingsGrouped[groupPosition];
            return new TextView(_context)
            {
                Text = group.Key
            };
        }

        public override bool IsChildSelectable(int groupPosition, int childPosition)
        {
            return true;
        }

        public override int GroupCount => _myThingsGrouped.Count;

        public override bool HasStableIds => true;
    }
}